Dependency on petroleum fuels has been an economic and environmental issue for some time. These factors have fostered the expansion of alternative fuels such as biodiesel.
Biodiesel is the name for a variety of ester-based oxygenated fuels made from vegetable oils, fats, greases, or other sources of triglycerides. It is a nontoxic and biodegradable substitute and supplement for petroleum diesel. Even in blends as low as 20% biodiesel to 80% petroleum diesel (B20), biodiesel can substantially reduce the emission levels and toxicity of diesel exhaust. Biodiesel has been designated as an alternative fuel by the United States Department of Energy and the United States Department of Transportation, and is registered with the United States Environmental Protection Agency as a fuel and fuel additive. It can be used in any diesel engine, without the need for mechanical alterations, and is compatible with existing petroleum distribution infrastructure.
Organic fuels, such as biodiesel, can include a wide variety of contaminants from different sources. For example, fuel frequently oxidizes and forms resinous materials such as varnishes commonly referred to as asphaltenes. As such, stability, especially by oxidative degradation, is a serious problem in hydrocarbon fuels. Biodiesel, as well as other hydrocarbon fuels, are known to form sticky deposits or gums both upon storage and under actual use conditions. These gummy residues can cause severe problems: for example, such deposits can cause valves to stick and such precipitates may cause filters to clog. These problems can adversely affect both the handling and combustion performance of the fuel. Among the different types of gasolines, pygas and cracked gasoline (both coker and FCC) are the most prone to oxidation and deposit formation.
Work in the area of organic fuel antioxidants has been performed over many years. One common class of antioxidants for this purpose is the phenylenediamines (PDA) used alone or in admixture with other materials. U.S. Pat. Nos. 3,322,520 and 3,556,748 teach that the phenylenediamine is usually N,N′-disubstituted with the substituents being either aliphatic or aromatic. U.S. Pat. No. 5,509,944 teaches that mixtures of PDA, hindered phenols and dimethyl surfoxide (DMSO) perform better than PDA alone. Phenylenediamines do not function well as stabilizers when the gasoline has a high acid number (>0.1 mg KOH/g gasoline). U.S. Pat. No. 5,169,410 teaches that the use of a strongly basic organic amine can, by preferentially reacting with acid moieties, increase the oxidative stabilizing efficacy of phenylenediamine.
U.S. Pat. Nos. 2,305,676 and 2,333,294 demonstrate that the use of N-substituted p-aminophenol derivatives and certain polyamines are effective in oxidative stabilization of a variety of gasolines. U.S. Pat. No. 4,648,885 discloses that a mixture of polyamines and N,N-diethylhydroxylamine is an effective stabilizer for distillate fuel oils.
However, despite these efforts to prevent the oxidative degredation of biodiesel and other organic fuels there remains a need to stabilize biodiesel more effectively.